Text and Photos by Sara Tanis, Department of Horticulture and Bert Cregg, Departments of Horticulture and Forestry, Michigan State University

Text and Photos by Sara Tanis, Department of Horticulture and Bert Cregg, Departments of Horticulture and Forestry, Michigan State University This mo...
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Text and Photos by Sara Tanis, Department of Horticulture and Bert Cregg, Departments of Horticulture and Forestry, Michigan State University

This month’s edition of Conifer Corner marks not only the beginning of a new year, but also a new series of articles on conifers for The Michigan Landscape. As we’ve noted before, the diversity of ornamental conifers almost defies description. Pinus mugo ‘Sherwood Compact’

In the previous series of Conifer Corner, we considered conifers based on the size classes as designated by the American Conifer Society (ACS). In this issue, aided and abetted by students in my Ornamental Conifers course (see endnote), we’ll discuss conifers in each of the conifer form classes designated by the ACS. The ACS recognizes eight form classes of conifers ranging from soldierstraight narrow upright plants to ground-hugging prostrate forms (see sidebar). Some form classes, such as weeping forms, are clear and definite, while the distinctions between others, such as broad-upright and narrow upright, can be subtle and plants may vary in their habit with age or growing conditions. Nevertheless, understanding form class is essential to effectively integrating conifers into a landscape. For example, narrow upright conifers are perfectly suited for year-round

Pinus mugo ‘Aurea’ combines color and form for interest (left). Tsuga canadensis ‘Gentsch White’ is a unique intermediate conifer. It has creamy needle tips and when placed with bright blues or yellows, it stands out even on the cloudiest days.

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screens or defining boundaries in a landscape. Weeping or irregular forms, in contrast, are often best used as single, attention-grabbing specimen plants. In this Conifer Corner, we will lead off our new series with “globose conifers”. Globose conifers are described by the American Conifer Society as those conifers that are “globe-like or rounded in general outline”. Globose conifers are easily as diverse as the other conifer forms; they come in all different sizes and colors, and have different growth rates and site preferences. This article will examine a few of the many uses for globose conifers and will introduce a few of the lesser known and versatile cultivars that are available to the landscaping community.

Size up the situation The ACS lists about 300 globe conifer cultivars; roughly 85% are in the dwarf or miniature size classes. Even within these size classes, however, growth can vary widely. There

is a big difference between Tsuga canadensis ‘Gentsch White’ which grows at rate of 3-6" per year and Tsuga canadensis ‘Aurora’ which grows at a rate of ½ to 1" per year. As always, growth rate is an important consideration in choosing a conifer appropriate for a given site. When surveying the site, consider whether planting close to a structure, along a path, or choosing a plant for a garden that might be viewed from a distance. This brings us to a second and equally important design parameter — scale. Be certain to provide a backdrop for dwarf globes, placing them in proximity to a pathway where people can stop and admire them or group them for a mounding effect if they will be viewed from a distance. Larger globe cultivars can achieve the single globe effect more easily from a distance or can be used to frame a doorway or walkway. No matter how you use them, be certain that you place them in such a way that they will carry out the design intent. Giving them too much or too little space can completely ruin the feel of your design and possibly lead to maintenance issues.

When placed close together, globose specimens will create a mounding effect. The addition of a contrasting blue specimen adds interest even from a distance.

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Informal or Formal? Many of the globose form conifers make excellent specimen plants. A globose conifer placed with pendulous or conical trees draws attention to itself without detracting from the beauty of its partners. When using different color combinations the different forms can complement each other. For example, placing the creamy-tipped Tsuga canadensis ‘Gentsch White’ with dark green Picea omorika can result in a striking effect that capitalizes on the differences in both form and color. Placed intermittently in borders, globes help to soften lines and add character. Dotted throughout a

When mixed with broad upright and spreading specimens, globose conifers provide a balancing focal point in between sky and ground (left). Pairing globes of different colors and textures can create a stunning affect (below). Triple threat. Picea omorika ‘Pimoko’ combines the bicolor needles and durability of Serbian spruce in a compact, globe form (inset).

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The Michigan Landscape™

garden, they help to break up long linear sections. Used in groups, they can lead the observer’s eye through the garden to different areas of interest. On the more prim and proper side of design, globes used in straight lines can provide framework for formal settings. Placing them in rows or offset from one another, they make excellent borders and can be used to frame geometric shapes and spaces. Another important element of formal gardens is the use of mirror imaging. Since most globe conifers are clonally propagated (grafted or produced from rooted cuttings), they are true to type, making it easy to find two specimens that are mirror images of one another. Cloned trees will have the same color, growth rate and growth habit, which make them an excellent uniform choice when framing a formal entry or sculpture.

In the formal Japanese-style garden, the globose Mugo pines and other vegetation block the sidewalk that is immediately behind them, all while providing a sense of peace and seclusion to the viewer (upper right).

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Picea abies ‘Horace Wilson’ (lower left) contrasts with other conifers at the Harper Collection at Hidden Lake Gardens (below). Grafting high on a standard adds another dimension to Picea abies ‘Little Gem’ (inset).

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Maintenance

Container Gardening When you think of container

designer’s imagination! Many

gardening, you might not

enthusiasts are pairing small

necessarily think of conifers. But, for

conifers with Japanese maples,

anyone looking for something other

flowering annuals, perennials and

than the traditional mums and

even herbs. In areas with milder

petunias on their porch, conifers

winters, such as the Zone 6 section

might be the answer. Many globose

of western Michigan, many of these

forms of conifers are available as

conifer container gardens are

dwarfs or miniatures and grow well

suitable to be outside all winter. In

in containers. Dwarf conifer

these areas, miniature conifer

gardens may be easily created in a

gardens can serve as an added

sturdy pot with good drainage

holiday decoration or a potted

using a potting mix which is high in

plant that provides interest all year

organic matter. The conifers must

long. If your area experiences

be consistently watered and receive

severe cold, the conifer gardens

adequate fertilizer (an annual slow

will survive in an insulated garage

release form is recommended). The

or potting house.

Another positive globose attribute is the fact that they require little if any pruning. Most are slow growing varieties with dense foliage that maintain their rounded form without any maintenance. When they are allowed to develop naturally, many globose conifers may become more spreading and often develop unique character with age. One concern with some globe conifers is breakage under heavy snow or ice loads. When possible, heavy snows can be gently brushed off with a broom. Avoid planting globe conifers under the eves of roofs where snow can accumulate. Conifer Container Gardening is becoming more and more popular as garden spaces and time become limiting.

possibilities are limited only by the

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The Michigan Landscape™

Suggestions Common globose conifers include: Pinus mugo ‘Sherwood Compacta’ and Thuja occidentalis ‘Globe’. While both of these are nice plants, there may be cause for concern regarding overuse. Mugo pine, in particular, is prone to spider mite infestation. There are many more globose cultivars available; we have listed several different genera to highlight the fact that many of the conifers that we love in the conical form are also available in the globose form. Abies balsamea ‘Nana’ A globose form of balsam fir. This plant forms a dense globe of dark, soft green needles. It is considered a dwarf. It grows 1–3" annually and will rarely get larger than 3' x 3'. This plant is salt Globe conifers such as these Abies balsamea ‘Piccolo’ are becoming more widely available in the trade (right). Pinus mugo ‘Sherwood Compact’ is a classic globe conifer (below).

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Conifer form classes recognized by the American Conifer Society (ACS) ACS Form Class

Description

1. Globose

Globe-like or rounded in general outline

2. Pendulous

Upright or mounding with varying degrees of weeping branches

3. Narrow upright

Much taller than broad; includes plants referred to as fastigiate, columnar, narrowly pyramidal or narrowly conical.

4. Broad upright

Includes all other upright plants which do not fit into categories 1-3

5. Prostrate

Ground-hugging, carpeting plants without an inclination to grow upward

6. Spreading

Wider than tall

7. Irregular

Erratic growth pattern

8. Culturally altered

Pruned or trained into formal or imaginative shapes, such as high grafts or standards

Source: American Conifer Society (www.conifersociety.org)

tolerant which makes it an excellent choice for sidewalk or parking lot plantings. This is a tried and true cultivar that has been used since the late 1800s. It is easy to find and hardy to Zone 3. Pinus strobus ‘Horsford’ A very compact globose white pine. Needles are lime green and soft. It is considered a dwarf and will grow to 3–6' in 10 years. This plant is unique in that it is propagated from seed — therefore color, form, and habit may vary among specimens. Hardy to Zone 3. Picea pungens ‘St Mary’s Broom’ A spreading globose blue spruce. This is an interesting specimen in that it retains its globe form while spreading low to the ground. It is a miniature conifer and grows less than one inch per year. It is perfect for tight spaces. Its intense blue color is a pick-me-up on cloudy days. Hardy to Zone 3.

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Chamaecyparis obtusa ‘Nana’ A globose form of Hinoki false cypress. It has very dark green fan-shaped leaves. It prefers partial shade. It grows one inch per year and is considered a miniature. It is excellent for container or rock gardens. Hardy to Zone 4. Larix laricina ‘Newport Beauty’ A globose form of American larch (Tamarack). This is a deciduous globe. It has soft blue-green needles that turn bright yellow in the fall. As with many larches, this plant’s primary attribute is the surge of bright growth in early spring. It grows less than one inch annually and is considered a miniature. It is another perfect choice for container or rock gardens. Hardy to Zone 2.

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Tsuga canadensis ‘Gentsch White’ A globose form of Canadian hemlock. This is one of the larger globose conifers; it grows 6–12" per year and is labeled an intermediate. It is also one of the most stunning of the globe conifers because of its creamy white branch tips. For a truly unique look, place this plant with a dark green screen. The branch tips are at their most intense color in fall and winter. It is suggested that the plant is sheared annually to encourage new white growth. Hardy to Zone 3. Pseudotsuga menziesii ‘Fletcheri’ A globose form of Douglas-fir. This globe requires full sun. It has light green soft needles typical of its species. It grows 1–6" per year and is labeled a dwarf. This plant is excellent for grouping. Hardy to zone 5.

Author’s note: Alert readers of Conifer Corner will notice a change to the byline starting with this edition. The current series of articles on conifer form classes was written by students in the MSU Ornamental Conifers course, which I taught this past fall. Each student was assigned to write an article on a different form class. I’ve edited the articles for consistency, but most of the content and some images are from the students. This month’s Conifer Corner co-author is Sara Tanis. Sara is a Horticulture graduate student from Ludington and her favorite conifer is Nootka falsecypress, Chamaecyparis nootkatensis. Dr. Bert Cregg is an Associate Professor in the Departments of Horticulture and Forestry at MSU. He conducts research and extension programs on management and physiology of trees in landscape, nursery, and Christmas tree systems. All photos used in this article are used by permission of Bert Cregg and may not be reused in any way without express written permission.

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